Rename machine_(u)int_t to mp_(u)int_t.

See discussion in issue #50.
diff --git a/stmhal/servo.c b/stmhal/servo.c
index 3da445f..8cd0a4e 100644
--- a/stmhal/servo.c
+++ b/stmhal/servo.c
@@ -194,7 +194,7 @@
     mp_arg_check_num(n_args, n_kw, 1, 1, false);
 
     // get servo number
-    machine_int_t servo_id = mp_obj_get_int(args[0]) - 1;
+    mp_int_t servo_id = mp_obj_get_int(args[0]) - 1;
 
     // check servo number
     if (!(0 <= servo_id && servo_id < PYB_SERVO_NUM)) {